Following the news that the BBC is trialling 4K and HDR on iPlayer with Blue Planet II, we get the latest on the broadcaster’s technological footing and future 4K TV plans.

The BBC isn’t alone in its recognition that 4K and HDR technologies are, in its words, “central to the future of high resolution TV”. And its aim to mutually deliver the two technologies (as well as wide colour gamut) isn't unique. But what it can offer over rivals such as SkyNetflix and Amazon Prime Video, is 4K HDR content for free, so long as you have a compatible TV, decent broadband connection and a TV license.

It’s been almost a year to the day since the BBC made a four-minute snippet of Planet Earth II temporarily available in 4K on its iPlayer catch-up service, and on Sunday, it’ll feature the entire series of Blue Planet II, not only in 4K but also with Hybrid-Log Gamma (a broadcast-friendly version of HDR the BBC co-invented with Japanese broadcaster NHK).

So what does this mean for the future of 4K and HDR, and how is the BBC getting involved?

A 4K trial, not a 4K service

No, it’s not quite time for couch potato 4K enthusiasts to stock the kitchen cupboards and buy new slippers. The 30-day access to Blue Planet II in 4K and HDR is simply a “trial” – the BBC's second if you count the short Planet Earth II clip – to help in its mission to reinvent itself for the next generation of TV.

Of course, jumping from mere minutes to several hours is no mean feat (even if it has taken the best part of a year), but crossing every finger and toe won’t change the fact that 4K BBC TV series are likely to trickle, rather than flood, through to iPlayer.

Why the hold up? Well, while not as complex as delivering a linear 4K broadcast channel (like, for example, the BT Sport Ultra HD channel), implementing 4K HDR content on to iPlayer still presents significant challenges.

As explained in a blog post, written by the BBC R&D team’s technologist Andrew Cotton, and Phil Layton, head of broadcast & connected systems, the trial version of the series was post-produced in HLG HDR, but it still needed HEVC encoding - with each episode taking about a day to encode.

With 11 different resolution versions having to be created to cater for varying internet bandwidths, it wasn’t quick work. But as Layton and Cotton write, “Our goal with these trials is always to leave the BBC with a better operational capability for the next trial. Each trial gets us closer to where we want to be…”

The stream dream: live broadcasts

…which is, ultimately, live broadcasts – just don't hold your breath.

As Layton explains: “iPlayer provides a very flexible tool for us to experiment with these technologies that allows us to deploy those on a programme-by-programme or series basis. Our next challenge is live production workflows into iPlayer. We want to make this a routine operation.

“A UHD channel… isn’t sustainable for what we have available right now. The OTT offerings offer a much more flexible route for delivering this content – and in a time scale we couldn’t match for terrestrial.” Still, wasn’t it Zuckerberg that said, “If you do the easier things first, then you can actually make a lot of progress”?

Live broadcasts look to be firmly in the pipeline, then – even if it’s more likely on the iPlayer platform than with a channel – with the BBC saying bitrates will be up to 50% higher.

More after the break

Plenty of 4K TV owners will benefit

A fair share of new and old 4K TVs from big manufacturers are compatible (the list of which can be found here) with this BBC 4K iPlayer trial. The BBC has said this list is being worked on constantly up until the event, so more compatible devices may be added in the coming days.

Lucky owners of these TVs won’t have to update the iPlayer app. And as the first trial allowed the BBC teams to work with device manufacturers to solve the interoperability issues identified during its testing, compatible TVs should, for this trial, automatically switch to an appropriate HDR mode when the HLG signal is detected.

The BBC claims some will allow a manual override via the menu settings, with the most helpful ones also showing a temporary graphic to indicate that they have switched mode.

No HDR TV? No problem

The fact that HLG signals are backwards-compatible means that those with non-HDR 4K TVs aren’t left out either, with this trial capable of delivering higher quality pictures to standard dynamic range 4K TVs that support the BT.2020 colour gamut.

As stated on the BBC blog post: “As the BBC iPlayer bitstreams use the HLG HDR format viewers do not necessarily need an HDR TV to benefit from the higher UHD resolution and wider colour gamut of the UHD iPlayer bitstreams.”  

In order to service as many people as possible, the BBC has purposely not locked it off to “HLG-supported” devices. Some TVs will deliver it in full 4K HLG, others will just be 4K.

And what about those with internet speed strain? The move from 8-bit AVC/H.264 compression (used for iPlayer’s HD streaming) to the 10-bit HEVC compression that supports HDR has made it possible to reduce the bitrate for a given resolution.

For example, while the highest HD quality currently delivered on iPlayer is 1280 x 720, 50 frames per second, at around 5mbps, HEVC can supposedly increase that to 1600 x 900, and add both wide colour gamut and HDR, for the same bitrate.

The argument is that while viewers need around 23mpbs to stream in 4K HDR, a 4K TV should still stream “better resolution, wide colour gamut and HLG high dynamic range” even with a slower internet speed.

No sign of surround sound

While immersive surround sound formats such as Dolby Atmos are being progressively attached to 4K, HDR content, the BBC hasn’t yet secured 5.1 surround sound.

It says it hopes to support surround sound in future iPlayer 4K trials, but for now we’ll have to settle for good ol’ stereo.

So, how does it look?

We were lucky enough to preview the final episode of Blue Planet II in 4K (but not HDR) at a London cinema. And it was more than enough to get us excited for the full series in 4K.

The texture of whales' skin was almost tangible, and the bright patterns of the fish are equally clear. At one point we thought we detected slight pixelation, only to realise it was miniscule particles moving though the sea.

But we're especially eager to see the combination of 4K resolution with HDR and wide colour gamut technologies – especially during the Coral Reefs episode. All we'll say is watch this space.

While the quality of physical formats are typically superior to that of streams, if Blue Planet II comes close to the quality of the Planet Earth II Ultra HD Blu-ray, we should be in for a, ahem, whale of a time.

Read more:

How to watch 4K video online and on TV

7 best 4K TVs to buy 2017

HDR TV: What is it? How can you get it?

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